1. Field of Invention
The present invention relates to chemical processes to yield zeaxanthin-like isomers, and more particularly, to the reactions of a naturally derived lutein pigment in the presence of polyhydric alcohols and alkali. The present invention also relates to the products produced by these synthetic methods, as well as the methods of using the pigments thus produced.
2. Description of Related Art
Carotenoids belong to an important class of natural pigments responsible for the coloration of many plant and animal species. These pigments are commonly used as coloring agents in food stuffs. In particular, adequate coloration is a major concern in the poultry industry where certain levels of pigmentation appeal to the consuming public.
To meet the expectations of the consumer, poultry producers have traditionally supplemented the diet of poultry with carotenoid containing meals of plant origin. The pigments extracted from these natural plants are capable of producing the desired yellow-orange color in poultry and poultry products, such as, in the skin of broiler chickens and egg yolks. A common plant source of carotenoids is marigold meal.
The family of carotenoid pigments consists of hydrocarbons, or carotenes, and of oxygenated carotenoids, or xanthophylls. In particular, it is the hydroxycarotenoids, or xanthophylls that have been shown to be most effective in attaining the desired level of pigmentation for use in poultry and poultry products. Lutein, a hydroxycarotenoid, is one of the most abundant, and widely used, natural carotenoids found commonly in marigold meal and its extracts.
Lutein, as well as other oxycarotenoids, occur naturally as esters of fatty acids, mainly as palmitic, myristic and stearic esters. However, the pigmenting efficiency of these xanthophylls are known to be increased in their free form where the ester linkage has been broken by means of a saponification reaction. Thus, saponification is generally performed following extraction of xanthophylls.
Various methods have been utilized to prepare xanthophyll concentrates from marigold meal. For example, in U.S. Pat. No. 3,523,138, marigold meal is reacted with an alcoholic alkali solution to remove the ester linkage. Following this saponification reaction, the mixture is generally solvent extracted to yield xanthophyll. Also, as described in U.S. Pat. No. 3,783,099, enzymatic hydrolysis of the cellulosic material of marigold meal can improve the extraction of the xanthophylls.
Carotenoids derive their intense color from the presence of a chain of conjugated double bonds in the chromophore. Moreover, it is the precise configuration of double bonds within the chromophore that gives different carotenoids their particular shades of yellow, orange or red. For instance, trans lutein, produces a yellow color with an absorbance maximum at 474 nm in hexane. If, however, trans luetin is isomerized, with only a single change in position of a conjugated double bond, an orange pigment is obtained with an absorbance maximum of 478 nm in hexane. Thus, in terms of the relative pigmenting efficiency, zeaxanthin yields more color per unit of pigment.
Although lutein is the predominate hydroxycarotenoid derived from marigold meal, it is its structural isomer, zeaxanthin, that has been shown to be more effective as a pigment, as compared to lutein, due to the precise bonding structure within the zeaxanthin chromophore. Typical extraction procedures of hydroxycarotenoids from marigold meal, however, yield approximately 82-88% of the less effective lutein and only about 3-6% of the more effective, zeaxanthin pigment.
More recently, fermentation reactions have been described in which alternative strains of Flavobacterium Multivorum result in production of zeaxanthin extracts with a 2 to 3 fold higher pigmenting efficiency, as compared with plant carotenoids, as described in PCT Int. Appl., WO91 03,571, dated Mar. 21, 1991 and issued to Applied Biotechnology, Inc. Generally however, the common source for zeaxanthin pigment is yellow corn and yellow gluten.
Chemical methods also have been described which result in the isomerization of lutein to zeaxanthin. Karrer and Jucker have described reacting lutein in the presence of sodium ethoxide and benzene to yield zeaxanthin. Karrer and Jucker, Helv. Chem. Acta, vol. 30, 366 (1947). Andrewes has also reported the isomerization of lutein to zeaxanthin under nitrogen, in the presence of methanol, potassium methoxide, and dimethylsulfoxide. A. G. Andrewes, Acta Chem. Scand., vol. B28, No. 1, 1137 (1974). Both reactions resulted in low yields. Consequently, these reaction processes are not suitable for industrial application.
Interestingly, Andrewes, et al., suggested that the reaction products can consist of several stereoisomers, rather than the trans zeaxanthin which is found in natural pigment sources. A. G. Andrewes, G. Borch, and S. Iiaaen-Jensen, Acta Chem. Scand., vol. B28, No. 1, 139 (1974). More recently, Maoka, et al., has confirmed the presence of three stereoisomers upon reaction of lutein in the presence of hydroxide. These include two optical isomers and a meso compound, namely (3R,3'R)-zeaxanthin, or trans zeaxanthin, (3S,3'S)-zeaxanthin, and (3R,3'S)-zeaxanthin. T. Maoka, A. Arai, M. Shimizu & T Matsuno, Comp. Biochem. Physiol., vol. 83B, No. 1, 121 (1986). Separation of these stereoisomers of zeaxanthin has also been reported. A. Ruttimann, K. Schiedt, and M. Vecchi, J. High Resolution Chromatography & Chromatography communications, Vol. 6, 612 (1983). The relative pigmenting efficiency of these stereoisomers, however, is unknown.
These reported reactions of lutein in the presence of a strong base and an organic solvent are generally considered to be catalytic, and require the absence of water or humidity. The presence of water in such a catalytic organic reactive phase would result in violent exothermic reaction, not suited for ordinary industrial use. However, recently Torres-Cardona, U.S. Pat. No. 5,523,494, disclosed the isomerization of lutein to zeaxanthin in a non-catalytic aqueous phase reaction. In this procedure, lutein is reacted with in a highly alkaline, aqueous solution for long periods of time to yield zeaxanthin. An alkaline, aqueous isomerization reaction also has been reported to lead to greater yields of zeaxanthin when performed under vacuum, as disclosed by Espinoza in Mexican Patent Application No. MX 942253.
Given the higher pigmenting efficiency of zeaxanthin relative to lutein, it would be desirable to produce zeaxanthin in a catalytic reaction suited for ordinary industrial use. Such a reaction would exclude the use of known toxins, such as benzene or dimethylsulfoxide, and would instead utilize non-toxic solvents. If these solvents were also non-aqueous, this should enhance the reaction rate yielding a more efficient overall reaction.
Therefore, there exists a need to synthetically produce zeaxanthin or a zeaxanthin-like pigment via an environmentally safe and economically efficient method suitable for industrial purposes. Moreover, the reaction should not only be temporally efficient in terms of the reaction time, but more importantly, the reaction should be efficient in terms of the yield of zeaxanthin produced per gram of lutein. Finally, the final zeaxanthin, or zeaxanthin-like, pigment should exhibit good stability as reflected in its shelf life.